CN107031037B

CN107031037B - Porous structure and method for manufacturing same

Info

Publication number: CN107031037B
Application number: CN201710034680.2A
Authority: CN
Inventors: R.L.兰东
Original assignee: Smith and Nephew Inc
Current assignee: Smith and Nephew Inc
Priority date: 2012-01-24
Filing date: 2013-01-23
Publication date: 2020-12-01
Anticipated expiration: 2033-01-23
Also published as: CN104168854A; CN104168854B; JP6208148B2; US20210308948A1; AU2013212268B2; US20180015675A1; EP2806820A1; CN107031037A; US10434718B2; AU2017202903A1; US20140371896A1; EP4122626A1; US11065819B2; AU2017202903B2; US9744728B2; EP4122626B1; EP2806820A4; WO2013112586A1; JP2017214660A; JP6643289B2

Abstract

The present disclosure allows for more controlled modification of input data to a Rapid Manufacturing Technology (RMT) machine to compensate for systematic errors in the manufacturing process, such as directional build differences, by performing the opposite effect of the input data. The modification is achieved with minimal introduction of unwanted deformations in other parts of the structure by decoupling the global scaling effect on the whole structure from the desired local effect on certain parts.

Description

Porous structure and method for manufacturing same

Technical Field

The present disclosure relates generally to porous structures produced by rapid manufacturing techniques and methods of manufacturing the same, and more particularly, to compensating for systematic errors in the manufacturing process of porous structures.

Background

Certain medical and orthopedic implants require strength for weight bearing purposes and porosity to promote bone/tissue in-growth. For example, many orthopedic implants include a porous section that provides a scaffold structure to promote bone in-growth during healing and a weight bearing section that is intended to allow the patient to walk more quickly. Rapid Manufacturing Techniques (RMT), in particular Direct Metal Fabrication (DMF) and solid free form fabrication (SFF), have been used to produce metal foams, which are used in medical implants or parts of medical implants. In general, the RMT method allows for the construction of structures, including tessellated/triangular entities and smooth entities, through a 3D CAD model. For example, the DMF technique produces three-dimensional structures layer at a time using powders that are solidified by irradiating a layer of the powder with an energy source such as a laser or electron beam. The powder is melted, or sintered by applying an energy source directed in a raster scan fashion at selected portions of the powder layer. After fusing the pattern in one layer of powder, another layer of powder is dispensed and the process is repeated, fusing between the layers until the desired structure is completed.

While DMF may be used to provide a dense structure that is strong enough to be used as a load-bearing structure in medical implants, the porous structures that are conventionally used employ an arrangement with uniform, non-random, and regular features that create a weak area where the struts of the three-dimensional porous structure traverse. The disclosures of international applications PCT/US2010/046022, PCT/US2010/046032, and PCT/U52010/056602 address these shortcomings by providing efficient methods of making three-dimensional porous structures and the structures themselves having randomized scaffold structures that provide improved porosity, improved strength including seamless joints between elements, improved connectivity, and beam characteristics without compromising strength. The entire disclosures of International applications PCT/US2010/046022, PCT/US2010/046032, and PCT/U52010/056602 are incorporated herein by reference.

However, the RMT construction process often does not accurately form the porous structure according to design input. In particular, due to the directionality of the build process for rapid manufacturing machines, objects built in the X-Y plane do not necessarily look the same as objects built in the Y-Z or X-Z planes. The Z dimension (or vertical direction) is more difficult to control when the build process is drawing in layers oriented in the X-Y plane. In other words, an aperture oriented in the X-Z plane should have a shape and size similar to another aperture in the X-Y plane, but a slightly different shape and size when constructed.

Although this difference is usually ignored in many cases, it is quite apparent when the constructed structures themselves are quite small, such as structures for in-growth in organisms. The slight differences in structures for in vivo growth caused by the RMT construction process may result in structures that do not optimally serve their purpose. For example, the structure may include struts that are prone to failure due to being thinner or more elongated than specified in the specification, or the structure may not have optimal porosity as thinner or more elongated struts due to the struts being thicker than specified.

In view of the above, there remains a need for effective methods to address the directional differences of structures built by RMT processes or other manufacturing processes that are affected by similar directional differences (e.g., affected by relative proximity to a heat source/sink or layer-by-layer build methods), particularly structures used for in-growth of living beings.

Disclosure of Invention

One aspect of the present disclosure is to compensate for orientation differences in the construction process of the RMT device by modifying features relative to the heat source/heat sink structure that affect the differences during the construction process of the RMT device.

Another aspect of the present disclosure is to provide a method of making features of a structure built in one plane have similar shapes and sizes as features built in another plane in an RMT device.

Another aspect of the present disclosure provides a structure having features that have compensated for orientation differences during construction of RMT devices.

According to one aspect of the present disclosure, there is provided a method for manufacturing a porous structure, the method comprising the steps of: generating a model of a porous structure, the generating step comprising the step of defining at least one strut of the porous structure, wherein the strut comprises a first node, a second node, and a body between the first node and the second node; assigning a local coordinate system to the strut, the local coordinate system having at least one direction perpendicular to a normal vector of a first plane; modifying the dimension of the at least one strut in the at least one direction, the modifying step not producing any change in the first plane; and fabricating the porous structure by exposing the fusible material to an energy source according to the model.

In one embodiment, the modifying step comprises the steps of: projecting a three-dimensional volume of the strut to the first plane such that the first and second nodes are in the first plane; applying a scaling factor to the dimension of the strut; projecting the three-dimensional volume projected in the first plane back to an initial position. In another embodiment, the modifying step does not change the location of at least one of the first node and the second node.

In one embodiment, the scaling factor is based at least on an error to be compensated for in a machine used to expose the fusible material to the energy source. In another embodiment, the first plane comprises a build plane of the machine. In another embodiment, the scaling factor is varied based at least on a distance relative to the build plane. In another embodiment, the dimension is selected from the group consisting of thickness and length.

According to another aspect of the present disclosure, there is provided a method for manufacturing a porous structure, the method comprising the steps of: generating a model of a porous structure, the generating step comprising the step of defining at least one strut of the porous structure, wherein the strut comprises a first node, a second node, and a body between the first node and the second node; assigning a local coordinate system to the strut, the local coordinate system having at least one direction perpendicular to a normal vector of a first plane; modifying the dimensions of the strut in the first plane; and fabricating the porous structure by exposing the fusible material to an energy source according to the model.

In one embodiment, the modifying step comprises the steps of: converting the local coordinate system to a coordinate system of the first plane; applying a scaling factor to the dimension of the strut; converting the coordinate system of the first plane to the local coordinate system. In another embodiment, the modifying step comprises the steps of: assigning an additional local coordinate system associated with at least one new node to the strut; converting the struts in the local coordinate system and the additional local coordinate system to a coordinate system of the first plane; applying a scaling factor to the dimension of the strut, the scaling factor corresponding to at least the additional local coordinate system; transforming struts in the additional coordinate system of the first plane to the local coordinate system.

In one embodiment, the modifying step is based at least on an error to be compensated for in a machine used to expose the fusible material to the energy source. In another embodiment, the first plane comprises a build plane of the machine. In another embodiment, the scaling factor is changed based at least on a distance relative to the first plane. In another embodiment, the dimension is selected from the group consisting of thickness and length.

Other advantages and features will become apparent from the following detailed description when read in conjunction with the drawings. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

Drawings

For a more complete understanding of the disclosed methods and apparatus, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein:

FIGS. 1A and 1B illustrate exemplary effects of affine scaling on porous structures;

FIG. 2 illustrates a support post having a local coordinate system independent of a machine coordinate system in accordance with aspects of the present disclosure;

FIG. 3 illustrates a first embodiment of a scaling strut in accordance with aspects of the present disclosure;

FIG. 4 illustrates a second embodiment of a scaling strut in accordance with aspects of the present disclosure;

FIG. 5 illustrates a third embodiment of a zoom post according to some aspects of the present disclosure;

FIGS. 6 and 7 illustrate an exemplary method of implementing the third embodiment of FIG. 5;

FIG. 8A illustrates the XY plane of the structure;

FIG. 8B is a Scanning Electron Microscope (SEM) image of an XY plane (as shown in FIG. 8A) of a portion of the porous structure at 25 times magnification;

FIG. 8C is a Scanning Electron Microscope (SEM) image of the XY plane (as shown in FIG. 8A) of the portion of the porous structure of FIG. 8B at 100 Xmagnification;

FIG. 9A illustrates the Z-plane of the structure of FIG. 8A;

FIG. 9B is a Scanning Electron Microscope (SEM) image of the Z-plane (as shown in FIG. 9A) of the portion of the porous structure of FIG. 8B at 25 times magnification;

FIG. 9C is a Scanning Electron Microscope (SEM) image of the Z-plane (as shown in FIG. 9A) of the portion of the porous structure of FIG. 8B at 100 times magnification;

FIG. 10 shows a graph of the average thickness of the individual pillars of the porous structure of FIG. 8B in the XY-plane and Z-plane.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated in schematic and partial views. In certain instances, details that are not necessary for an understanding of the disclosed methods and apparatus or that render other details difficult to perceive may have been omitted. Of course, it should be understood that this disclosure is not limited to the particular embodiments set forth herein.

Detailed Description

The present disclosure provides a method for addressing directional differences in a freeform fabrication machine that fabricates cellular structures. Preferably, the improved porous structure of the present invention is formed by utilizing a free-form fabrication method, including Rapid Manufacturing Techniques (RMT), such as Direct Metal Fabrication (DMF). Typically, in RMT or freeform fabrication, a model or computer readable file defining a desired structure or a desired structure is provided to a computer-assisted machine or device having an energy source, such as a laser beam, that melts or sinters the powder to build the structure one layer at a time according to the provided model.

A detailed description of selective laser sintering techniques can be found in U.S. patent nos. 4,863,538, 5,017,753, 5,076,869, and 4,944,817, the entire disclosures of which are incorporated herein by reference. Current practice is to control the manufacturing process by computer using mathematical models generated with the aid of a computer. Accordingly, RMT (such as selective laser remelting and sintering techniques) can directly fabricate solid bodies or 3D structures using a variety of materials.

Due to the machine arrangement of the heat source/sink and the build-up of one layer or plane at a time, it is more difficult to control the build-up process in a direction perpendicular to the layer or surface. In this way, features of the structure in a direction perpendicular to the build plane do not match features in the model and the build plane. For example, FIGS. 8A-8C, 9A-9C, and 10 demonstrate this directional difference for a particular RMT machine. Referring to fig. 8B-8C and 9B-9C, the posts constructed by this machine in the XY plane (shown in fig. 8B-8C) have a different surface roughness and appearance than the posts constructed in the Z plane (shown in fig. 9B-9C), where the posts in the Z plane are rougher and appear "hazier". Referring to fig. 10, the machine constructed pillars in the Z plane slightly thicker than those in the XY plane, on average about 50 microns, although both groups of pillars should have the same thickness according to the input model.

As such, each RMT machine typically has a system difference factor. For example, the strut thickness may be affected by the intensity of the laser light, which may be proportional to the distance from the laser (e.g., heat source). In addition, the build platform of the device and the structure being built may also serve as a heat sink. For example, the portion closer to the heat sink is more likely to have the correct size. In addition, the relative complexity of the flow of heat from the heat source to the heat sink also contributes to the directional difference of the machine. In a porous metal structure, it is at least more difficult to make the vibrating molecules of the pillars heat up the adjacent metal molecules (if the metal molecules are not strongly bonded), thus reducing heat dissipation.

While not intending to be bound by theory, there are several possible explanations for the differences in system orientation. For example, if the heat is too high, the melt pool may lose its shape and flatten out. In this case, adjacent materials are bonded to each other so that the part is thicker than expected from the model. On the other hand, if the heat is too low, the bonding between layers and between adjacent particles in the X-Y plane may be less than optimal, thereby producing thinner pillars than desired according to the model. Depending on the surface roughness (based on some of the other factors mentioned), the cleaning process used to clean off excess powder can affect the shape and size of the porous orifice. This is particularly true when the underside is very rough (high surface area) and etching techniques are used (more sensitive to high surface area).

In preferred embodiments, the term "heat source" generally refers to a laser, the term "heating zone" generally refers to a layer of fused powder, and the term "heat sink" generally refers to a build platform or build feature used for the same purpose. In addition, as described above, heat flow associated with the heat sink also affects build up differences. For example, the poor heat flow region may receive only 80% of the projected heat, which is a 20% reduction compared to the model. Similarly, the medium heat flow receives 90% of the projected heat, thereby resulting in a 10% reduction in size compared to the model, and the high or optimal heat flow region receives the full heat, thereby producing build features that are according to the model or slightly thicker. The poor heat flow region is typically farther from the build platform than the medium and high heat regions. The medium thermal zone is further from the build platform than the high thermal zone. The high heat zone is closest to the build platform.

One possibility is to compensate for such deviations of a particular RMT machine. For example, if the RMT machine used is known to build a percentage thicker structure in the vertical plane than the model, the operator may manually compensate for this difference by modifying the model or instructing the machine to build a percentage thinner structure in the vertical direction than the model. The method is suitable for large structures. However, problems can arise in smaller structures that require precise dimensions (such as structures intended to promote and/or support tissue in-growth). For example, struts that are too thin are prone to failure, and struts that are too thick or elongated will not provide an optimal range of pore sizes for tissue ingrowth.

Referring to FIG. 1A, a structure 10 has a strut 12 of length A and thickness B. If a particular machine typically builds a thinner thickness B of the support post 12 than specified by the input model, a three-dimensional software application that generates or assists in generating the input model for the RMT machine may allow for the application of an affine scaling factor to the input model to account for/account for some build direction difference in the RMT machine, such as a support post 12 that is thinner than specified. Unfortunately, any adjustment to the thickness B of the posts 12 by affine scaling can result in a change in the location of holes (such as holes 14) in the structure 10. For example, referring to FIG. 1B, when an affine scaling factor γ is used to increase the thickness B of the strut 12, resulting in a thickness B ', the length A is also affected by the same factor γ, resulting in a length A'. In other words, affine scaling can be expressed as follows:

A’=γA B’=γB。

thus, affine scaling results in an increase to structure 10 in FIG. 1B. As the structure 10 grows, the position of the holes 14 changes, which is reflected in a greater length A'. Thus, such affine scaling links a desired change in B 'to an undesired change in a'. When only local scaling is required, the global scaling effect of affine scaling produces an undesirable deformation of the entire structure. If the structure 10 is a larger structure for a larger application, then changes in the location or size of the holes 14 may have minimal effect. However, if the structure 10 is a smaller structure requiring precise dimensions, such as a structure intended to promote and/or support tissue in-growth, any minor changes and movements from the ideal dimensions of the input model may result in significant structural defects that render the structure 10 unusable for its intended application. For example, after affine scaling, the pores 14 may be larger than the desired optimal pore size to promote tissue growth after affine scaling.

Examples of larger structures for large applications typically include features of interest greater than about 1mm-2 mm. Furthermore, the term "large" generally refers to the ratio between dimensions and their tolerances. For example, if the directional difference is about 0.050 to 0.25mm and the tolerance is +/-0.3mm, then compensation may not be required since the difference is within an acceptable tolerance range. On the other hand, if the tolerance is +/-0.1mm for the same orientation, the error is not appropriate and needs to be compensated.

The present disclosure also provides a method of compensating for directional differences inherent in freeform fabrication machines or other machines processes affected by similar directional differences while minimizing undesirable deformation of the modified structure. In one embodiment, the modified features are not grown proportionally, but rather the process adds one or more layers of material to compensate for the differences. In another embodiment, the layer of material is generally less than 1/10 millimeters.

According to one aspect of the disclosure, one approach to addressing the directional difference includes non-uniform affine scaling, such as scaling only in the direction that needs compensation (e.g., the Z-direction). One method of performing non-uniform scaling includes compressing or expanding cells of a model of a structure. In a preferred embodiment, expanding the structure in the Z-direction is equivalent to contracting the structure in the X-Y direction and enlarging the struts or the entire structure until the X-Y direction appears unaltered. Similarly, shrinking the structure or strut in the Z direction is equivalent to expanding in the X-Y direction, and then shrinking the strut or structure until the X-Y direction appears unaltered.

After compression or expansion, the struts of the model may be defined to impart thickness and form to the structure. In one embodiment, the apertures preferably appear oval and are compressed (or elongated) in the Z-direction. The model can then be scaled in the Z-direction so that the holes end up in their initial positions and the struts are proportionally thicker. This method requires the modification of the entire cell structure or lattice when a portion of the structure is to be modified.

According to another aspect of the present disclosure, another method of resolving directional differences includes: certain portions of the structure are individually scaled by decoupling the overall or global scaling effect on the entire structure from the desired local scaling effect on the particular portion.

One embodiment of disassociating the global zoom effect and the local zoom effect includes: some parts of the structure that require local scaling are assigned a local coordinate system. In a preferred embodiment, one axis of the local coordinate system is oriented along the body of the strut and the other axis is generally along the deformation direction, e.g. the Z-direction. Other reversible coordinate systems may be used to achieve the effect of decoupling, as long as they allow the struts to return to their original positions. The assigned local coordinate system allows scaling the parts by an optimal or desired amount in a desired direction using linear algebra to compensate for machine variations. After assigning the local coordinate system, the three-dimensional (3D) volume of the portions is projected onto a build plane (e.g., a transverse or X-Y plane) such that the positions of the portions to be scaled are within the plane. These portions are then modified (e.g., increased or decreased in thickness) in a desired direction (e.g., the Z direction) by an optimal or desired amount to compensate for machine build variations in that direction. After modifying the portions in the transverse plane, the scaled portions project back to their original positions, where the scaled portions are larger or smaller (as needed) in the Z-direction independently of the build plane (e.g., the X-Y plane). Thus, local scaling does not change the position of these scaled portions relative to the entire structure, thereby minimizing unwanted deformation of the structure during the scaling process.

In another embodiment, instead of projecting the 3D volume of the portions to be scaled to the transverse plane, the portions to be scaled may be converted to the transverse plane. In a preferred embodiment, the transformation is a rotation and translation that places the new coordinate system and all related objects in correspondence with another coordinate system (commonly referred to as the "global" coordinate system). When in the transverse plane, the thickness of the portion may be modified (e.g., increased or decreased) as desired in a direction perpendicular to the build plane. The scaled portions are then converted back to their original positions, where the scaled portions are enlarged or reduced in the Z-direction (as needed) independently of the build plane (e.g., the X-Y plane). In this embodiment, other areas of the scaled portion may be slightly deformed within the build plane (e.g., the X-Y plane of the machine coordinate system) in addition to being in the X-Y plane of the local coordinate system. Because a particular feature is scaled in the Z-direction when in a transverse plane or in a global coordinate system, the feature may be slightly distorted in the Z-direction when the inverse transformation is performed. In one embodiment, the angle of the struts relative to the global coordinate system determines the slight distortion, e.g., the magnitude of the expansion/contraction factor applied to the Z direction. For example, if the thickness is increased by 10%, the horizontal strut is increased to 110% of its thickness. However, for a strut at 45 degrees to the horizontal, the thickness increases to 105% of its thickness, and the vertical strut remains unchanged. In other embodiments, a fixed value (e.g., 50 or 150 microns) may be assigned to compensate for an increase or decrease in strut thickness or length as needed, rather than a certain percentage.

Alternatively, by moving the z-coordinate of the point defining the pillar/porous structure in the model based on the direction of the feature to be modified relative to the horizontal, a local scaling effect can be performed without producing an overall change. For example, if the surfaces of the posts are multi-faceted, and those facets are parallel to the build platform, the coordinates can be moved perpendicular to the surfaces by a full amount of compensation. On the other hand, if the faces are perpendicular to the build platform, the coordinates are not moved perpendicular to their surface. This embodiment does not require that the struts be defined in the model. Achieving local scaling by moving the z coordinate may require significant computational resources and manipulation of the three-dimensional file of the structure.

According to another aspect, the present disclosure addresses directional differences in RMT machines, particularly caused by the relative distance of the portions from the heat source/sink in the RMT machine. In some instances, portions of the structure tend to build thicker closer to the heat source than more distant portions of the structure, even though the input model dictates the same thickness regardless of distance from the heat source. Similarly, portions of the structure may be thicker at more distant discrete heat sinks than portions closer to the heat sinks. To compensate for differences caused by build distance relative to the heat source, a gradient scaling factor or a stepped expansion may be utilized. The gradient scaling factor may be constant or vary depending on the machine or application. For example, the structure may have a scaling gradient at or near the heat source that is 80% of the thickness of the input model and gradually increases to 100% at a sufficient distance away from the heat source. Alternatively, according to some aspects of the present disclosure, the portion at or near the heat source may be modified to build 80% thickness, 85% at about 100 microns from the heat source, 90% at about 200 microns from the heat source, and so on. These numbers are merely exemplary, as it is preferred to select a scaling gradient or a stepped expansion based at least on the specific directional differences and/or operating conditions of the particular machine being used.

In particular embodiments of methods for altering the shape of certain features of a structure to account for/account for variations in the direction perpendicular to the build plane or layer, the features that need to be altered (e.g., posts) are isolated and individually scaled to avoid undesirable deformation of other features of the structure (e.g., holes). This is preferably achieved by decoupling the global scaling effect on the whole structure caused by the affine scaling of the struts from the desired local scaling effect on the individual features or struts.

In one embodiment, there is a structural model input for the RMT machine with ideally placed struts and nodes to define the desired aperture configuration, as is the case with machines building features of a structure from a model without any build differences. In a particular embodiment, referring to FIG. 2, the strut 200 preferably includes a first end 202, a second end 204, and a continuous elongated body 206 between the first end 202 and the second end 204. The body 206 has a selected or predetermined thickness and length. In a preferred embodiment, the first end 202 and the second end 204 serve as a node of the strut 200, wherein the node may include an intersection between an end of a first strut and the body of a second strut, an intersection between an end of a first strut and an end of a second strut, and/or an intersection between an end of a first strut and any other portion of the overall structure.

For clarity and simplicity of maintenance, only the strut 200 of the larger structure (not shown) is provided in the drawings and is discussed herein for exemplary purposes. It should be understood that various aspects of the present disclosure may be applied to modify a plurality of legs or various portions of a structure to be constructed by an RMT machine. In one embodiment, the post 200 is defined such that there is no difference as the RMT machine can consistently produce a perfect part as dictated by the input model. In a preferred embodiment, defining the ideal strut includes identifying all surfaces and/or volumes of each region between nodes. For example, this includes certain characteristics of the body 206 defining the strut 200. These characteristics include strut diameter, longitudinal shape, cross-sectional shape, size, shape profile, strut thickness, material characteristics, strength curves, or other characteristics. This is an ideal input model for the strut 200.

Referring to FIG. 2, in one embodiment, the ideal model of the support column 200 is an assigned local or nodal coordinate system 208 that is different from a machine coordinate system 210. The local or nodal coordinate system 208 allows the mast 200 to be scaled to compensate for build direction differences for a particular machine without introducing undesirable distortion to the larger structure (not shown) of which the mast 200 is a part. For example, certain RMT machines may have system expansion issues, such as build direction differences in a direction perpendicular to the build plane, where the machine tends to produce structures with thicker struts or other features that are thicker near the heat source and thinner in the direction perpendicular to the build plane away from the heat source. The relative distance from the heat sink or heat flow also contributes to systematic expansion errors of the machine, as described above.

One way to minimize undesirable distortion during compensation is to maintain the position of the

struts

202 and 204 while modifying the thickness of the body 206 of the strut 200 using the local coordinate system 208. Preferably, linear algebra can be used to scale the thickness of the body 206.

Referring to fig. 3, in one embodiment, the 3D volume of strut 200 is projected onto a plane, where no changes are needed so that

nodes

202 and 204 lie in the plane. The projection is shown by arrow 212. Some 3D characteristics are maintained when the support post 200 is projected onto a new plane. In one embodiment, this plane is a build plane or machine coordinate system 210, such as a transverse or X-Y plane, where in some cases the energy absorbed by the portions of the structure in that plane from the heat source of the machine is substantially the same. The body 206 has a thickness 214 prior to projection that is the same as a thickness 216 when the support post 200 is projected into a plane having the machine coordinate system 210. Once in this plane, body 206 expands or contracts as appropriate to compensate for build direction differences for the particular machine, resulting in body 206'. For example, if the machine exhibits a tendency to build thicker pillars about 25% thicker toward the heat source in a direction perpendicular to the build plane (e.g., the Z direction), then a scaling factor of 80% may be applied in this perpendicular direction to obtain a thickness of about 100% as dictated by the input model, rather than a greater thickness of 125%. The compensation accounts for systematic errors in the manufacturing process by performing an inverse effect on the input data. Depending on the build differences exhibited by a particular machine, the scaling factor may be applied in a gradient or step-wise manner as described above. After the desired scaling factor has been applied, the strut 200 may be projected back to its original position, as indicated by arrow 218. The strut 200 (now with the body 206') is independently scaled in the Z direction (or direction requiring compensation) independently of the X-Y direction (or build plane). When the support post 200 is scaled in a build plane with a machine coordinate system 210 and projected back into the local coordinate system 208, the positions of the

nodes

202 and 204 are unchanged. In this way, the thickness scaling of body 206 occurs locally and does not cause any undesirable deformation of the positions of

nodes

202 and 204. In the present embodiment, the support post 200 is scaled relative to the machine coordinate system 210.

While not wishing to be bound by theory, the following examples provide a general analogy to the projection process described above. The struts can be viewed as a piece of bread sliced according to the first coordinate system, which results in the slices being angled. To project the bread loaf to a second plane, the slices are placed next to each other as if they belong to a precisely flat bread loaf. In this new plane, the new bread loaf appears shorter and larger than before being sliced in the first coordinate system. In the new bread block of the second coordinate system, each slice may have a different height depending on how flat the bread block before the slice is. The slice of the new patch in the second coordinate system (i.e., the new plane) is stretched in the desired direction by the desired amount. The slice projections are then returned to the first coordinate system, where the slices are placed next to each other in their angular positions, the entire surface patch now being stretched in the desired direction.

Referring to FIG. 4, in another embodiment, the strut 200 may be scaled relative to the local coordinate system 208. Specifically, as indicated by arrow 212, the strut 200 is translated to a plane that does not require alteration, such as the transverse plane described above. In a preferred embodiment, a signal such as [ T ] is utilized]And [ T]^-1The transformation matrix of (a) implements the transformation, wherein [ T [ [ T ]]Is rotated and/or translated to the machine coordinate system 210, as indicated by arrow 212, and [ T ≡ T]^-1Is rotated and translated to the node coordinate system 208 as indicated by arrow 214. When the support 200 is transformed to a plane with a machine coordinate system 210, the local coordinate system 208 of the support 200 is the same as the machine coordinate system 210. An exemplary transformation matrix that may be used is a motion matrix; but other suitable conversion matrices may be used. In other embodiments, a kaiser angle, euler angle, or any other method of rotation and translation to a desired position may be used. After converting the support post 200 to a plane having a machine coordinate system 210, the thickness of the body 206 may be scaled as desired depending on whether the machine differences result in an increase or decrease in the thickness of the body 206. Scaling or modifying at least one dimension of body 206 results in body 206' having a different dimension. After performing the desired scaling, the support post 200' is converted back to the local coordinate system 208, as indicated by arrow 214. In the present embodiment, the support post 200 is scaled relative to the local coordinate system 208. The strut 200 now having the body 206' has a new thickness compared to the body 206 before scaling, wherein the positions of the

nodes

202 and 204 remain less distorted than in the case of the affine factor applied.

In some instances, when more than one strut is present in a structure, machine deviation may require scaling the thickness of one strut and scaling the length of that strut. Various aspects of the present disclosure may be employed to address different directional requirements individually without associating changes with the overall structure. Referring to fig. 5A, there is a structure 500 including a strut 502 having a thickness 504 and a length 506, the structure 500 scaled according to some aspects of the present disclosure to the structure 500 of fig. 5B including a strut 502 having a thickness 504 'and a length 506'. Fig. 6 depicts an exemplary process of scaling the thickness 504 of the strut 502, and fig. 7 depicts an exemplary process of scaling the length 506 of the strut 502. In a preferred embodiment, thickness 504 is scaled independently of length 506. In other words, the scaling of the disassociation may be expressed as follows:

504’=γ504 506’=ξ506

where γ ≠ ξ, and γ and ξ may be > 1, < 1, or = 1.

Referring to fig. 6, a first step for known build errors in the fabrication of the compensation structure 500 depicted in fig. 5 includes defining

nodes

508 and 510 of the post 502. This includes defining the positions of

nodes

508 and 510 relative to structure 500 and/or the distance between

nodes

508 and 510. The process further includes the step of identifying all surfaces and/or volumes of each region between

nodes

508 and 510. For example, this includes certain characteristics of the body 512 defining the post 502. These characteristics include strut diameter, longitudinal shape, cross-sectional shape, size, shape profile, strut thickness, material characteristics, strength curves, or other characteristics.

The process further includes assigning the strut 502 a local coordinate system 514 that is different from the machine coordinate system 516. In the preferred embodiment, machine coordinate system 516 is the coordinate system of a feature (the main heat sink of the machine), e.g., the coordinate system within the machine that specifies that the systematic build errors need to be corrected. The positions of

nodes

508 and 510 are maintained as thickness 504 is scaled, thereby introducing an opposite effect from the input data to the machine to counteract systematic errors in the manufacturing process while minimizing undesirable deformation of structure 500. As described above, thickness compensation may be achieved with respect to a machine coordinate system or with respect to a local coordinate system.

To scale the thickness 504 relative to the local coordinate system 514, the strut 502 is translated to a plane that does not need to be changed, such as the transverse plane with the machine coordinate system 516 as described above. In a preferred embodiment, a signal such as [ T ] is utilized]And [ T]^-1The transformation matrix of (a) implements the transformation, wherein [ T [ [ T ]]Is rotated and/or translated to a machine coordinate system 516, as indicated by arrow 518, and [ T ≡ T]^-1Is rotated and translated to the node coordinate system 514 as indicated by arrow 520. An exemplary transformation matrix that may be used is a motion matrix. Thickness 504 is scaled in machine coordinate system 516 as needed to yield thickness 504'. The scaling factor preferably indicates whether the thickness of the body 512 is increased or decreased based at least on machine build differences. After performing the desired scaling, the strut 502 is converted back to the local coordinate system 514 as indicated by arrow 520. After scaling the post 502, the post 502 has a new thickness 504' compared to the old thickness 504.

To scale the thickness 504 relative to the machine coordinate system 516, the 3D volume of the strut 502 is projected onto a plane, where no changes need to be made, such that the

nodes

202 and 204 lie in the plane. In one embodiment, this plane is a build plane or machine coordinate system 516, such as the transverse or X-Y plane described above. Once in this plane, the body 512 expands or contracts as appropriate to compensate for build direction differences for the particular machine. The compensation accounts for systematic errors in the manufacturing process by performing an inverse effect on the input data. Depending on the build differences exhibited by a particular machine, the scaling factor may be applied in a gradient or step-wise manner as described above. After modifying thickness 504 as needed, strut 502 is projected back to its original position, where thickness 504' is greater or less in the direction that needs compensation, independent of the build plane.

Referring to fig. 7, in one embodiment, length 506 may be modified with minimal introduction of undesirable distortions in structure 500 depicted in fig. 5A by scaling the positions of nodes 508 and/or 510 in machine coordinate system 516 to preserve thickness 504 and converting struts 502 back to local coordinate system 514. Before converting the strut 502 to the machine coordinate system 516, it is assigned new nodes 508 'and 510' with their own local coordinate system 522. Using the transformation matrix [ T ] described above for the original positions of nodes 508 and 510]And a transition matrix [ T ] for the new positions of nodes 508' and 510_new]The two local coordinate

systems

514 and 522 are converted to the machine coordinate system 516, where [ T [ ]_new]Is rotated and/or translated from the local coordinate system 522 to the machine coordinate system 516. By using [ T ]]And [ T_new]Is rotatedThe change is represented by arrow 524. Referring to fig. 7, after the strut 502 is converted to the machine coordinate system 516, the local coordinate system 514, the local coordinate system 522, and the machine coordinate system 516 are matched to each other as shown. After scaling is performed in the machine coordinate system 516 to provide the strut 502 with the new length 506' and new

corresponding nodes

518 and 520, [ T ] is utilized_new]^-1Only the new local coordinate system 522 is converted back to the machine coordinate system 514, where [ T ] is_new]^-1From the machine coordinate system 516, the coordinate system is rotated and transformed to the node coordinate system 522 as indicated by arrow 526. This conversion results in a scaling of the length 506' in the data input into the machine for manufacturing being compensated. After scaling and conversion back to the local coordinate system 522, the strut 502 has new nodes 508 'and 510' that reflect the change in length 506 as compared to the

old nodes

508 and 510, while the thickness 504 remains the same.

Alternatively, the projection method described with reference to fig. 3 may also be used to compensate for the length of the strut 502. In this embodiment, the other areas of the scaled (i.e., lengthened or shortened) portion may appear slightly deformed in addition to the X-Y plane of the build plane. The angle of the struts relative to the build plane causes this slight deformation, e.g., the magnitude of the expansion/contraction factor applied in the Z-direction. For example, the length scaling of the horizontal struts with the projection method achieves the full effect of the length scaling, but the vertical struts do not experience any lengthening effect, but rather become thicker. The length of the strut as an angle may be scaled based on knowing the angle and percentage of elongation such that the vertical strut does not experience any length scaling, while the horizontal strut does experience a full amount of scaling. In the meantime, the scaling factor applied to the length of the angled strut may be changed accordingly, such as by multiplying the cosine value of the angle by the full amount of the scaling factor applied to the horizontal strut. "horizontal" and "vertical" are relative to the heat source of a particular machine.

In one embodiment, scaling in the X or Y direction may be performed independently if the object is scaled in the Z direction without affecting the features in the X or Y direction. In a preferred embodiment, it is desirable to identify whether the strut is most aligned with X or Y, and then use the angle between the projected strut and the closest axis in the X-Y plane. The elongation process may be applied to the direction and proportional to the calculated angle.

The order of modification or compensation (e.g., thickness or length) is preferably immaterial. Embodiments of the present disclosure align a local coordinate system and a global coordinate system. Thus, many of the problems associated with sequencing are no longer problematic.

The process of compensating for build variations of the machine may occur before the defined pillars are written to the computer files to be read by the RMT machine. Alternatively, it may be done while the pillars are defined. In another embodiment, compensation for systematic errors of the manufacturing process may occur after the ideal model has been converted into a computer readable file for the RMT machine and transmitted to the machine (where the machine settings are added). In a preferred embodiment, the compensation is performed after the definition of the struts.

According to another embodiment, a computer program product may be used to implement or perform an embodiment of the present disclosure. For example, the computer program product preferably includes a non-transitory computer-readable medium having code for assigning a local coordinate system to certain portions of the structure requiring local scaling. The medium further includes code to project a three-dimensional (3D) volume of the portions to a build plane (e.g., a transverse or X-Y plane) such that the positions of the portions to be scaled are within the plane. The medium further includes code to modify (e.g., increase or decrease the thickness or length or any other expansion compensation desired) the portions by an optimal or desired amount in a desired direction (e.g., the Z-direction) to compensate for machine build variations in that direction. The medium further includes code to project the scaled portions back to their original positions after modifying the portions in the transverse plane.

In another embodiment, the medium further comprises code that translates to a transverse plane. The medium further includes code to modify the dimensions of the portion in the transverse plane as desired (i.e., in a direction perpendicular to the build plane). The medium also includes code to convert the scaled portions back to their initial positions where they are larger or smaller (as needed) in the Z-direction independently of the build plane (e.g., X-Y directions).

In accordance with another embodiment, a system is provided that includes a processor coupled to a memory, wherein the processor is configured to implement or perform an embodiment of the present disclosure. For example, the processor is configured to assign a local coordinate system to certain portions of the structure that require local scaling. The processor is further configured to project a three-dimensional (3D) volume of the portions to a build plane, such as a transverse or X-Y plane, such that the positions of the portions to be scaled lie within the plane. The processor is further configured to modify (e.g., increase or decrease the thickness or length or any other expansion compensation desired) the portions by an optimal or desired amount in a desired direction (e.g., the Z-direction) to compensate for machine build variations in that direction. The processor is further configured to project the scaled portions back to their original positions after modifying the portions in the transverse plane.

In another embodiment, the processor is further configured to translate to a transverse plane. The processor is further configured to modify the dimensions of the portion in the transverse plane as desired (i.e., in a direction perpendicular to the build plane). The processor is further configured to convert the scaled portions back to their initial positions where they are larger or smaller (as needed) in the Z-direction independently of the build plane (e.g., X-Y directions).

Embodiments of the system of the invention may include one or more computer systems for implementing the various methods of the invention. An exemplary computer system may include a Central Processing Unit (CPU), which may be any general purpose CPU. The present invention is not limited by the architecture of the CPU or other components of the system of the present invention, so long as the CPU and other components support the operation of the present invention as described herein. The CPU may execute various logical instructions according to embodiments of the present invention. For example, the CPU may execute code to determine the various embodiments described above.

Further, the exemplary computer system may also include Random Access Memory (RAM), which may be SRAM, DRAM, SDRAM, or the like. Embodiments may also include Read Only Memory (ROM), which may be PROM, EPROM, EEPROM, and the like. The RAM and ROM hold user and system data and programs, as is well known in the art.

The exemplary computer system also includes an input/output (I/O) adapter, a communications adapter, a user interface adapter, and a display adapter. In some embodiments, I/O adapters, user interface adapters, and/or communications adapters may enable a user to interact with a computer system to input information and obtain output information that is processed by the computer system.

The I/O adapter preferably connects one or more storage devices, such as one or more of a hard disk drive, Compact Disk (CD) drive, floppy disk drive, tape drive, etc., to the exemplary computer system. The memory device may be employed when the RAM is insufficient to meet the memory requirements associated with storing data for the operation of the above-described components (e.g., the demand arbitration system). The communications adapter is preferably adapted to couple the computer system to a network, which can enable information to be entered into and/or exported from the computer system via a network (e.g., the internet or other wide area network, a local area network, a public or private switched telephone network, a wireless network, a combination of any of the foregoing). User interface adapters connect user input devices (such as keyboards, pointing devices, and microphones) and/or output devices (such as speakers) to the exemplary computer system. The display adapter is driven by the CPU to control display contents on the display device, for example, to display a model of a structure to be modified by the above-described respective embodiments.

It should be appreciated that the present invention is not limited to the architecture of an exemplary computer system. For example, any suitable processor-based device may be used to execute the various elements described above (e.g., software for presenting a user interface, a claim arbitration system, etc.), including but not limited to personal computers, notebook computers, computer workstations, and multiprocessor servers. Furthermore, embodiments of the invention may be implemented on Application Specific Integrated Circuits (ASICs) or Very Large Scale Integration (VLSI) circuits. Indeed, any number of suitable structures capable of carrying out logical operations in accordance with embodiments of the present invention may be employed by those of ordinary skill in the art.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the scope of the appended claims is intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A method for manufacturing a porous structure with a machine, the method comprising the steps of:

a. generating a model of a porous structure to be fabricated by the machine, the generating step comprising the steps of: a strut defining the porous structure, wherein the strut comprises a first node, a second node, and a body between the first node and the second node;

b. assigning a local coordinate system to the pillar, the local coordinate system being different from a machine coordinate system defining a build plane of the machine;

c. correcting the difference in orientation of the machine by modifying the dimensions of the support column in a direction perpendicular to the build plane, wherein the modifying step does not produce any change in the position of the first and second nodes; and

d. fabricating the porous structure with the machine by exposing a fusible material to an energy source according to another model with modified struts;

wherein the modifying step comprises the steps of: projecting a three-dimensional volume of the strut to the build plane such that the first and second nodes are in the build plane; applying a scaling factor to the dimensions of the struts projected to the build plane to produce a scaled three-dimensional volume; and projecting the scaled three-dimensional volume in the build plane back to an initial position in the local coordinate system.

2. The method of claim 1, wherein the dimension is selected from the group consisting of thickness and length.

3. The method of claim 1, wherein the scaling factor is based on at least an error associated with the directional difference to be compensated for in a machine used to expose the fusible material to the energy source.

4. A method for manufacturing a porous structure with a machine, the method comprising the steps of:

c. correcting directional discrepancies of the machine by modifying dimensions of the struts in a direction perpendicular to the build plane; and

wherein the modifying step comprises the steps of: projecting a three-dimensional volume of the strut to the build plane such that the first and second nodes are in the build plane; applying a scaling factor to the dimensions of the struts projected to the build plane to produce a scaled three-dimensional volume; and projecting the scaled three-dimensional volume in the build plane back to an initial position.

5. The method of claim 4, wherein the modifying step is based at least on an error to be compensated for in a machine used to expose the fusible material to an energy source.

6. The method of claim 4, wherein the dimension is selected from the group consisting of thickness and length.

7. The method of claim 4, wherein the scaling factor is varied based at least on a distance relative to the build plane.